Field of the Invention
The present invention relates to pulverulent compositions of a complex between an acid and a metal and the method of preparation thereof.
Description of the Related Art
Methionine, an essential amino acid, and HMTBA, an analogue of methionine, find very extensive applications in humans as a food supplement or medicinal product, as well as in animal feed. Their metal salts, for example the calcium, magnesium or zinc salts, in solid form, may be preferred. They can also make up for deficiencies of elements or trace elements. The best-known HMTBA salt is the dicalcium salt, comprising two moles of HMTBA equivalent per mole of calcium corresponding to the formula (HMTBA)2Ca.
A method is known from EP140865A for preparing calcium salts of HMTBA, consisting of more than two and less than ten moles of HMTBA equivalent per mole of calcium. These salts are obtained by reacting HMTBA with a source of calcium selected from calcium oxide (CaO), calcium hydroxide (Ca(OH)2), calcium carbonate (CaCO3) as well as an HMTBA salt, for example the salt (HMTBA)2Ca. HMTBA is generally in highly concentrated aqueous solution, with which the source of calcium is mixed, then the reaction medium thus obtained is dried at a temperature of the order of 70° C. The reaction medium of HMTBA with the source of calcium is, however, very viscous and sticky; it is therefore very difficult to homogenize in mixers or reactors equipped with conventional stirring systems, and at the end of reaction it is necessary to carry out drying in situ so as to be able to empty the reactor.
Recycling of HMTBA calcium salt, for example the salt (HMTBA)2Ca, to the source of calcium before bringing it in contact with the HMTBA allows improvement in the consistency of the reaction medium and makes it easier to carry out the method as mentioned in EP140865A. But, as taught by U.S. Pat. No. 4,335,257, this improvement is observed for a proportion by weight of at least 20% of said salt relative to the reaction medium, and to achieve an acceptable consistency it may be necessary for this proportion to reach 80% of the reaction medium. Such a recycle ratio of finished product in the reaction medium reduces the productivity of an industrial installation considerably and necessitates appreciable oversizing of the mixer/reactor for a desired production capacity.
WO03/011822A2 proposes a method for preparing organic acid salts, in particular calcium salts, starting from said organic acid and calcium hydroxide and/or calcium oxide, in which the organic acid is deposited on an inert support before adding the source of calcium to it. Despite the presence of this support, it is essential to introduce the two reactants by successive addition in order to allow the reaction medium to dry between the two additions. This procedure greatly increases the residence time in the mixer and also requires considerable oversizing of said mixer for a given production capacity. Moreover, the inert support remains in the dry finished product, where it represents from 30 to 50 wt % of the total mass, which reduces the titre of active ingredient to that extent and thus generates extra costs in using the product (storage, transport, metering, etc.).
A solution that partly allows the aforementioned obstacles to be circumvented, but without requiring a support or other excipient, might be to use a simple method for preparing one or more HMTBA salts by means of an extruder. The advantage of such a method would be to perform rapid mixing of the acid and the metal in a short time and with shearing forces that would allow the HMTBA salt formed to be extruded without difficulty. However, a method of this type would lead to the formation of thin strands at the outlet from the extruder die that are incompatible with the particle sizes required in the end applications for the HMTBA salt, for example the production of animal feed products. Moreover, it would still be necessary to dry the product, which finally leads to adding two extra unit operations of drying and grinding of the HMTBA salt for it be usable.
FR 1469803, US 2006/0251765 and U.S. Pat. No. 6,287,627 describe methods for preparing salts between the anion of an acid and a metal cation, said method comprising a step for obtaining an aqueous solution of said salt, and a step of spray-drying of said aqueous solution.
These two-step methods make it possible to obtain salts in the form of powders, the granulometry of which allows direct use of said powders, for example for making animal feed products. However, the latter introduce, in addition to the reaction step, an additional step of drying. Moreover, they do not allow a high dry extract of the reaction medium; a high dry extract would lead to clogging of the equipment used.